It's the oldest and most clichéd of metaphors, but when it comes to global warming, it's the only one that really works: We're in a desperate race. Politics is chasing reality, and the gap between them isn't closing nearly fast enough.

Shaken scientists see every prediction about the future surpassed by events. As Martin Parry, co-chair of the Intergovernmental Panel on Climate Change, told reporters this month, "We are all used to talking about these impacts coming in the lifetimes of our children and grandchildren. Now we know that it's us."

The panel's chair, Rajendra Pachauri, offered the planet an absolute deadline: We need to be producing less carbon dioxide—which is to say burning less coal, gas and oil—by 2015 at the latest, and after that we would need "very sharp reductions" or else there is no hope of avoiding an eventual temperature increase of 2 degrees Celsius and the accompanying prospect of catastrophe.

Such news has finally begun to penetrate the bubble of denial that has surrounded Washington for two decades. President Bush, after ignoring the issue for six years, has convened a conference of the major carbon-emitting nations to begin considering . . . something. Bush said in a speech yesterday that "we acknowledge there is a problem," but few expect the process to amount to much; cynics see it as a way to derail ongoing U.N.-sponsored talks for a firm agreement on reducing emissions.

The only real hope is for decisive legislation from Congress; activists are calling for a law that commits the United States to early cuts, closes all coal-fired power plants and auctions the right to pollute so that we can raise the revenue to fund the transformation of our energy system. President Bush won't sign such a law, so it doesn't have to pass this fall; we're working to set the stage for 2009, when a new leader takes over.

It will take a movement to force that kind of change—a movement as urgent, and one to which people are as morally committed and willing to sacrifice, as the civil rights movement was a generation ago. Last spring, I worked with six college students to put together StepItUp07.org. In the course of 12 weeks, with almost no money, we helped put together 1,400 rallies in all 50 states demanding action. This fall we're trying again.